How can I make a custom carrierwave post processor?

Question

I need to do some post processing on a file upload that isn't images - in paperclip I can have a custom post processor, but I can't find any way to do this in carrierwave.

Ruby 1.9.3, Rails 3.2.7 and CarrierWave 0.6.2.

Answer 1

The OP's question was how to process files which are not images.

Please have a look at this source file on GitHub: carrierwave/lib/carrierwave/uploader/processing.rb and check the comments.

You'll have create your own CarrierWave uploader sub-class and mount it in your model like this:

  def MyModel < ActiveRecord::Base

    # this is where the uploaded file will be available in your model,
    # as a `MyUploader` instance:
    #
    mount_uploader :uploaded_file, MyUploader

    ... 
  end

Please note that it's mounted on the ActiveRecord attribute :uploaded_file. This means when you access :uploaded_file from your model, you will get an instance of your CarrierWave uploader for the particular file which was uploaded.

You can simply define your processing inside your uploader as follows:

  class MyUploader < CarrierWave:Uploader::Base
    process :my_custom_processing => [param1,param2,param3]

    def my_custom_processing(param1,param2,param3)
      ...
      # e.g. you could call a method which is defined elsewhere,
      # which operates on a file:
      my_nifty_file_processor( self.uploaded_file ) 
      #
      # or you could just do this directly:
      uploaded_data = self.uploaded_file.read
      ...
    end
  end

Inside my_nifty_file_processor, you would simply call read on the object that gets passed in to read the file.

CarrierWave lets you call read on any Uploader instance (= any instance of an uploaded file) and it will read that file.

One more Tip:

Sometimes you need to access the ActiveRecord model within your uploader, for which the file was uploaded.

Simply access it inside your uploader code like this:

      self.model

This lets you store additional information about the uploaded file, such as format, directly in your AR model.

Answer 2

I wrote a blog post on how to create custom post-processor to create thumbnails of videos, maybe you will find it useful.

https://prograils.com/posts/video-encoding-processor-for-carrierwave/